DE102010035251A1 - High-temperature glass solder and its use - Google Patents

Abstract

The present invention relates to glass solders and composites, which are particularly suitable for high temperature applications, and their applications e.g. B. in fuel cells or sensors in the exhaust gas flow of internal combustion engines. The crystallizing glass solder is characterized by a thermal expansion coefficient in the temperature range from 20 ° C to 300 ° C of 8.0 · 10–6 K – 1 to 12.6 · 10–6 K – 1 and a hemispherical temperature of 850 ° C to 1100 ° C off.

Description

The present invention relates to glass solders, in particular crystallizing glass solders, and to composites which are particularly suitable for high temperature applications and their applications.

Glass solders are usually used for the production of joint connections, in particular to connect glass and / or ceramic components with each other or with components made of metal. In the development of glass solders, their composition is often chosen so that the thermal expansion coefficient of the glass solder corresponds approximately to that of the components to be joined together in order to obtain a permanently stable joint. Compared with other joining compounds, for example those made of plastic, such based on glass solders have the advantage that they can be made hermetically sealed and can withstand higher temperatures.

Glass solders are generally often made from a glass powder, which is melted during the soldering process and results in the heat transfer with the components to be joined the joint. The soldering temperature is usually chosen approximately equal to the so-called hemispherical temperature of the glass or can usually differ by ± 20 K from this. The hemisphere temperature can be determined in a microscopic procedure with a hot stage microscope. It indicates the temperature at which an originally cylindrical specimen has been melted together to form a hemispherical mass. The hemisphere temperature can be assigned a viscosity of about log η = 4.6, as appropriate literature can be found. If a crystallization-free glass in the form of a glass powder is melted and cooled again so that it solidifies, it can usually also be remelted at the same melting temperature. For a joint connection with a crystallization-free glass solder, this means that the operating temperature to which the joint connection can be permanently exposed must not be higher than the soldering temperature. In fact, in many applications, the operating temperature must still be significantly lower than the soldering temperature, since the viscosity of the glass solder decreases with increasing temperatures and a glass which can flow to some extent can be forced out of the joint at high temperatures and / or pressures, so that it can fail its service.

For this reason, glass solders for high-temperature applications usually have a soldering temperature or hemispherical temperature which is still significantly above the later operating temperature. A problem that can arise due to the significantly higher soldering temperature compared to the later operating temperature is the damage to the components to be joined together. Therefore, glass solders are desired, which indeed have the lowest possible soldering temperature, but still allow the highest possible operating temperature. This means that the desired glass solders should be reflowable after a first soldering only at a higher temperature than the soldering temperature.

With pure non-crystallizing glass solders this is not easy to achieve. Glass solders that meet such requirements, however, can be obtained if the base glass during the soldering process at least partially crystallized, the crystalline phases significantly different from the base glass properties z. B. respect. The thermal expansion may have, but in particular the temperature required for the re-melting is usually well above that of the base glass. The properties of an at least partially crystallized glass solder can be directly influenced by the composition of the original base glass, but also by suitable fillers, which usually have a crystalline structure and are added to the solder glass. The mixture of glass solder and filler is called composite in the sense of this application.

A field of application of such glass solders and / or composites are z. B. joining compounds in high-temperature fuel cells, which z. B. can be used as an energy source in motor vehicles. An important fuel cell type, for example, the so-called SOFC (solid oxide fuel cell), which can have very high operating temperatures of up to about 1100 ° C. The joint connection with the glass solder is usually used for the production of fuel cell stacks, d. H. used for connecting multiple individual fuel cells to a stack. Such fuel cells are already known and are being continuously improved. In particular, the trend in current fuel cell development is generally to lower operating temperatures. Some fuel cells already reach operating temperatures below 800 ° C, so that a lowering of the soldering temperatures possible and due to the then low temperature load of the SOFC components in the soldering process is also desirable.

A major role in fuel cell development comes in the glass solders, which are already the subject of the following disclosures.

The DE 19857057 C1 describes an alkali-free glass ceramic solder having a thermal expansion coefficient α _(20-950) of 10.0 × 10 ^-6 K ^-1 to 12.4 × 10 ^-6 K ^-1 . The solder described therein contains MgO of 20 to 50 mol. %. High MgO-containing glasses are in practice highly sensitive to crystallization, which leads to fast and strong crystallizing compounds. With such rapid and strong crystallization, it is difficult to ensure good wetting of the material to be joined by the glass solder. However, this is necessary in order to be able to provide a joining connection which optimally satisfies the respective requirements.

Also glass ceramic solders are in the US 6,532,769 B1 and US Pat. No. 6,430,966 B1 described. These are designed for soldering temperatures of about 1150 ° C and contain 5 to 15 mol% Al ₂ O ₃ . Such high soldering temperatures are undesirable for modern fuel cells because they place too much stress on the metallic substrate materials and other temperature-sensitive materials.

The DE 10 2005 002 435 A1 includes composite solders consisting of an amorphous glass matrix and a crystalline phase. The glass matrix has high contents of CaO, but this leads to relatively high viscosities and high dielectric losses.

In the DE 10122327 A1 describes a glass solder from the system BaO-CaO-SiO ₂ for the combination of ceramics and metals in the high temperature range. The glasses have a CaO content of up to 30 wt .-%. High CaO contents can lead to an increased unwanted crystallization.

In the glass systems of the invention, the dominant crystallization mechanism is surface crystallization. If these are provided, as usual, from pulverulent mixtures of the starting components for producing the joint connection, the crystallization generally takes place before the softening temperature of the soldering glass is reached, ie well before the soldering temperature is reached. When reaching the soldering temperature, the solder is thus already partially crystallized, which means that the required soldering temperature often has to be chosen well above 1100 ° C, since it must be adapted to the higher melting point of the partially crystallized solder glass. At such high temperatures, metallic components of the joint compound can lead to undesirable oxidation reactions. A resulting oxide layer of a certain thickness can flake off during the soldering process and thus prevent a tight connection. Furthermore, at such high soldering temperatures, the evaporation of Cr from steels, which are often part of the components of the joint connection, increases. Evaporating Cr can lead to the so-called poisoning of the electrolyte of an SOFC and thus negatively affect the performance.

For the purposes of this disclosure, the term "crystallizing glass solder" includes glass solders which at least partially crystallize during the brazing process or, preferably, in a subsequent process, although amorphous, glassy phases may also be present in the glass braze. Accordingly, the state of the glass solders after processing is referred to as crystallized, even if amorphous, glassy phases may still be present in the glass solder.

The invention is therefore based on the object to provide a suitable solder glass available, as well as a crystallizing glass solder or a composite including this solder glass, which is to be processed at a soldering temperature of about 1100 ° C, whose viscosity after completion of the soldering process at operating temperatures to about 900 ° C is still so high that it is not pressed out of the joint compound and / or flows out of this and its thermal expansion in the temperature range of 20 ° C to 300 ° C α _(20-300) in the crystallized state in the range of 8.0 × 10 ^-6 K ^-1 to 12.6 × 10 ^-6 K ^-1 and is thus adapted to steels used in fuel cells, but also to oxide ceramics, in particular ZrO ₂ and / or Al ₂ O ₃ ceramics ,

The object is further that the linear thermal expansion of the crystallizing glass solder in the glassy state and in the crystallized state does not have too great a difference, since otherwise by the crystallization process mechanical stresses in the fusion arise that jeopardize their stability.

The object is achieved by the glass solders and / or composites according to the independent claims. Preferred embodiments will be apparent from the dependent claims.

All other percentages mentioned are, unless stated otherwise, in% by weight based on oxide.

According to the invention, the gas solder contains 45% to 60% BaO, 25% to 40% SiO ₂ , 0% to 15% B ₂ O ₃ and optionally up to 18% SrO. Furthermore, optionally at least one alkaline earth oxide RO is selected from the group MgO and / or CaO and / or ZnO and / or BeO up to 10% in the glass solder according to the invention. By the content of SrO and the alkaline earth oxides RO, the crystallization properties of the glass solder can be controlled.

Furthermore, optional components, which may be up to 10%, are oxides selected from the group Al ₂ O ₃ and / or Ga ₂ O ₃ and / or In ₂ O ₃ and / or Y ₂ O ₃ and / or La ₂ O ₃ . These too can influence the crystallization properties and, in interaction with the alkaline earths, are used according to the invention for setting the desired crystallization properties.

Optionally, at least one oxide RO ₂ selected from the group TiO ₂ and / or ZrO ₂ and / or HfO ₂ with up to 5% is furthermore contained in the glass solder according to the invention. These oxides can act in particular as nucleators for the crystallization.

Further additives are possible. For the purposes of the invention, the term glass solder includes both the amorphous base glass, which is used as solder glass before the soldering process, and the material resulting from the base glass during the soldering process, which may inter alia be glassy, crystallized, partially crystallized, glass ceramic or in any other form.

The inventors have recognized that in particular a high Al ₂ O ₃ content of a glass solder has a negative effect on its properties. The Al ₂ O ₃ content is therefore limited in the present invention to up to 2% Al ₂ O ₃ .

The limited proportion of Al ₂ O _{3 of} the glass solder according to the invention has the effect that unwanted crystal phases such as BaAl ₂ Si ₂ O ₈ , so-called barium feldspates, can not form increasingly. Of the compound BaAl ₂ Si ₂ O ₈ exist two phases with very different coefficients of thermal expansion: Celsian with a thermal expansion coefficient of 2.2 · 10 ^-6 K ^-1 and Hexacelsian with a coefficient of thermal expansion of 7.1 · 10 ^-6 K ^{- 1} , wherein the hexacelsian is stable at higher temperatures than the celsian. When a glass solder is cooled, for example in a joint connection of a fuel cell, a conversion of the Hexacelsian phase into the Celsian phase may occur below 300 ° C. This conversion is associated with a volume jump of about 3% or more, whereby strong mechanical stresses occur and the joint connection can be destroyed. The glass solder according to the invention prevents the formation of these crystal phases and thus increases the reliability of the joints.

Another unwanted crystal phase is Mg ₂ Al ₄ Si ₅ O ₁₈ , also known as cordierite, which can be formed in the presence of Al ₂ O ₃ and MgO. Cordierite has a very small thermal expansion coefficient of about 1.5 · 10 ^-6 K ^-1 . Also, this crystal phase does not fit with its elongation behavior to the majority of high-temperature applications such as joining compounds in fuel cells. The crystallizing glass solder according to the invention also prevents the excessive formation of cordierite phase due to its limited content of Al ₂ O ₃ and MgO.

The content of SiO ₂ determined to a large extent the melting temperature, causes in the connection with B ₂ O ₃ but the formation of a stable glass. In order to fulfill the task of a low melting temperature of the glass solder, the glass solder according to the invention contains a maximum of 40% SiO ₂ .

The B ₂ O ₃ content influences not only the crystallization behavior but also the melting behavior and thus the glass melt positively. On the other hand, an excessively high B ₂ O ₃ content can have a negative effect on the chemical resistance. Furthermore, with B ₂ O ₃ contents above 15%, boron oxide evaporations can occur from the glass solder, which is likewise undesirable.

The glass solder according to the invention further contains 42% to 60% BaO (in wt .-% based on oxide). For barium oxide levels greater than 60%, the glass solder may tend to form barium silicate crystals. At a barium oxide content of less than 42%, the desired thermal expansion coefficient can not be achieved. Depending on other glass constituents and their atomic weights, the crystallization-stable glasses with thermal expansion according to the invention are obtained at a barium oxide content of 42% to 52% or, in another embodiment, at a barium oxide content of 47% to 50%.

The crystallizing glass solder _{according to the} invention has a linear thermal expansion coefficient α _{(20-300), G} in the glassy state of 6 · 10 ^-6 K ^-1 to 11 · 10 ^-6 K ^-1 , where the index G on the amorphous, glassy Condition related size features. This means that the coefficient of thermal expansion of the base glass and / or of the glass solder that has not crystallized during the soldering process is the abovementioned Value range. In the crystallized state, ie when the glass solder at least partially crystallizes during the soldering process, it preferably has a thermal expansion coefficient α _{(20-300), K} , of 8 · 10 ^-6 K ^-1 to 12.6 · 10 ^-6 K ^-1 , wherein the index K denotes the size related to the crystallized state.

Typically, the crystallization process is therefore associated with a small increase in the thermal expansion coefficient. Due to the small differences in the thermal expansion before and after crystallization, however, only slight mechanical stresses are introduced into the fusion by the crystallization process, which do not jeopardize their stability.

Preferably, the glass solder SrO and / or the said alkaline earth oxides RO may contain. With these components can z. B. influence on the crystallization behavior of the glass solder are taken. Surprisingly, it has been found in the glass solders according to the invention that the tendency to crystallize can be suppressed by the addition of RO, in particular of MgO, in exchange for SiO ₂ . Another positive effect is that the dielectric loss can be reduced by glasses containing RO. Furthermore, the melting temperatures and the glass transition temperature can be reduced by the network-converting alkaline earth oxides. The content of RO also causes an increase in the coefficient of thermal expansion and thus provides a simple way to adapt the glass solder to the components to be fused. The glass solder according to the invention therefore preferably contains in total up to 20% MgO and / or CaO and / or SrO, particularly preferably 2% to 15%.

The glass solders according to the invention are preferably free of alkali metals. Alkali metals can adversely affect the electrical insulation properties, but also reduce the chemical resistance of the glass solder.

Another preferred optional additive is ZrO ₂ in an amount of up to 5% (in% by weight on an oxide basis). As is known, ZrO ₂ acts as a nucleating agent and its addition can thus influence the crystallization behavior as well as the crystal size. The composition of the solder glass is preferably adjusted so that it crystallizes slowly. If it were already crystallizing very strongly, adequate wetting is often not given. In particular, the solder glass is to be introduced during the manufacture of a joint in general in non-crystallized or partially crystallized form in the joint to be soldered, since the temperature required for the wetting of the components to be fused is then lower.

A preferred embodiment of the glass solder contains 42% to 52% BaO, 24% to 31% SiO ₂ , 0% to 11% B ₂ O ₃ , 14% to 18% SrO, 0% to 5% CaO, 0% to 10% MgO, 0% to 10% R ₂ O ₃ and 0% to 5% RO ₂ , wherein the sum of CaO and MgO and R ₂ O ₃ and RO _{2 is} from 0% to 19%. It is preferable to use Al ₂ O ₃ as R ₂ O ₃ and to dispense with the addition of RO ₂ . The thermal expansion coefficient α _{(20-300), K} in the crystallized state in this embodiment is preferably> 9 · 10 ^-6 K ^-1 .

The inventors have recognized that, in particular in this embodiment, there is a eutectic in the ternary system BaO-SrO-SiO ₂ , in which the crystalline phase SrBa ₂ Si ₃ O ₉ precipitates. The percentage weight ratio between the oxides BaO, SrO and SiO ₂ is chosen such that the composition with respect to these three oxides is in the range of the described eutectic. As a result, glasses can be realized with a short temperature interval, less than 300 ° C., between sintering and flow.

In the composition interval according to this embodiment, it is possible to avoid excessive crystallization of the partially crystalline glasses by the addition of R ₂ O ₃ as well as the precipitation of unwanted crystal phases. Also, crystallization can be completely suppressed, thus providing a stable glass solder. In the case of the partially crystalline glasses, the crystalline fraction is below 35% by weight. Excessive crystallization during the joining process would lead to an increase in viscosity and shift the soldering temperatures to values greater than 1100 ° C. The doping of the glasses with RO ₂ can promote the partial crystallization and increase the strength of the joint compound. Depending on the temperature control during the soldering process, the glasses can be present as glass as well as partially crystallized glass ceramic. The crystalline phase is preferably SrBa ₂ Si ₃ O ₉ and BaSi ₂ O ₅ . Formation of trydimite can be avoided by the addition of CaO.

Another preferred embodiment contains 47% to 50% BaO, 35% to 39% SiO ₂ , 5% to 15% B ₂ O ₃ , 0% to 10% CaO, 0% to 10% MgO, 0% to 5% TiO ₂ and 0% to 5% ZrO ₂ .

In this case, the molar ratio of the contents of SiO ₂ to BaO _{2 is} preferably ≦ 2.5, particularly preferably ≦ 2. The thermal expansion coefficient α _{(20 × 300), K} in the crystallized state is preferably from 7 × 10 ^-6 K in this embodiment ^{. 1} to 11 · 10 ^-6 K ^-1 . The inventors have recognized that at higher ratios, the thermal expansion coefficient of the glasses may be too low.

In a particularly preferred embodiment, it is provided that the molar ratio of SiO ₂ to BaO is less than 2, and very particularly preferably less than 1.7.

The crystallizing glass solder may further contain up to 0.5% (in weight percent on an oxide basis) of V ₂ O ₅ and / or Sb ₂ O ₃ and / or CoO. These additives cause a significant increase in the adhesion of the glass solder on metallic substrates.

The glass solder according to the invention preferably has a hemispherical temperature of 850.degree. C. to 1100.degree. C., and can accordingly be used for the joining compound at about this temperature.

The crystallizing glass solder according to the invention is generally prepared by the solder glass is ground after its preparation in a conventional glass melt to a glass powder, the z. B. can be introduced into the joint connection in the form of a dispensable paste or a presintered molding. The crystallizing glass solder produced from the molten solder glass preferably has an amorphous, non-crystalline state before the soldering process.

The present in powder form crystallizing glass solder before or during further processing to the above pastes and sintered bodies according to the invention additionally up to 35% (in wt .-% on an oxide basis, based on the total mass of glass solder and filler) of a preferably crystalline filler also in powder form be added so that a composite is obtained. The properties of the composite can be positively changed and adjusted by the filler compared to the properties of the filler-free glass solder. Thus, the filler whose particle size distribution and, of course, its proportion z. As the thermal expansion and the rate of crystallization.

Sanbornite (BaSi ₂ O ₅ ), 3YSZ (yttrium stabilized zirconium oxide), wollastonite (CaSiO ₃ ) or enstatite (Mg ₂ Si ₂ O ₆ ) or any combination of these substances is preferably used as the filler. The addition of this filler makes it possible to adapt the thermal expansion coefficient of the crystallized base glass α _{(20-300), K} , as can be seen in Table 2 in Example B1. The thermal expansion coefficient in the temperature range 20 to 300 ° C of the crystallized composite α _{(20-300), K} is in the range 8 · 10 ^-6 K ^-1 to 12 · 10 ^-6 K ^-1 , which in the temperature range 20 ° C to 750 ° C α _{(20-750), K} in the range of 9.5 × 10 ^-6 K ^-1 to 14.5 × 10 ^-6 K ^-1 .

The composites of the invention preferably have a hemisphere temperature of 850 ° C to 1020 ° C.

Optimum strengths of a joint connection are achieved when the solder is optimally adapted in the thermal expansion to the materials to be fused. Furthermore, even a change in the thermal expansion coefficient due to the crystallization process should not result in excessive stresses in the solder. On the one hand, the glass solder according to the invention ensures this by avoiding unwanted phases, as already explained; on the other hand, the glass _solders according to the invention and the composite produced therefrom are characterized in that the difference in the thermal expansion α _(20-300) before and after the crystallization process is less than 2 × 10 ^-6 K ^-1 and preferably less than 1 × 10 ^-6 K ^-1 .

The at least partially crystalline state of a composite after processing is referred to as crystallized analogous to the filler-free crystallizing glass solder, even if amorphous glassy phases may still be present.

Due to its physical properties, the crystallizing glass solder according to the invention is particularly suitable for the production of high-temperature-resistant joint compounds. High-temperature-resistant in the sense of the invention means a temperature range of more than about 650 ° C. Such joining compounds can be used particularly advantageously in fuel cells, in particular SOFCs. An example of an application in fuel cells is to connect individual SOFCs to a SOFC stack. Further fields of application are sensors in combustion units, for example automotive applications, marine engines, power plants, aircraft or in space technology. A preferred application is the use of the inventive glass solder and sensors in the exhaust system of automobiles.

However, the crystallizing glass solder and / or composite according to the invention can also be used for the production of sintered bodies with high temperature resistance. Production methods of sintered bodies are well known. In general, while the starting material of the glass solder according to the invention in powder form is mixed together, mixed with a generally organic binder and pressed into the desired shape. Instead of the powders of the starting materials, an already molten glass according to the invention can also be ground and mixed with the binder. The pressed glass-binder body is then brought to sintering temperature whereby the binder can burn out and sinter the glass components together at the sintering temperature. The sintered body thus obtained may then be brought into contact with the components to be joined and connected by a soldering process and / or connected to these.

The use of sintered bodies during soldering has the advantage that the sintered body is a shaped component and can be brought into almost any desired geometries. An example frequently used form is a hollow cylinder, which can be introduced together with an electrical contact pin in lead-through openings of metal components in order to obtain by soldering a preferably hermetically sealed glass-metal leadthrough with an electrically insulated contact pin. Such glass-metal bushings are used in many electrical components and are known in the art.

A further preferred application of the crystallizing glass solder and / or composite according to the invention is the production of films which contain the glass solder and / or the composite. Such films are similar to the sintered body described above, but can be made largely flexible. From them shapes can be punched out and used in an advantageous manner to connect flat components together.

The invention will be described in more detail below with reference to the properties of crystallizing glass solders according to the invention as well as comparative examples.

α_(20-300),G

linearer thermischer Ausdehnungskoeffizient von 20°C bis 300°C

T_g,G

Glasübergangstemperatur, oder kurz Übergangstemperatur

EW_G

Erweichungstemperatur, bei dieser Temperatur beträgt der Logarithmus der Viskosität 7,6

ρ_G

Dichte

First, the solder glass was melted in a molten glass. The following properties were measured on the solder glass, which is generally present in block glass, at least in solid form, the index G characterizing the physical properties determined on the solder glass.

α _{(20-300), G}

linear thermal expansion coefficient from 20 ° C to 300 ° C

T _{g, G}

Glass transition temperature, or short transition temperature

EW _G

Softening temperature, at this temperature, the logarithm of the viscosity is 7.6

ρ _G

density

The composition of the solder glasses and their physical properties are summarized in Table 1.

After the characterization of the solder glass, the powder glass solder is generally produced from the solder glass by a grinding process. In the present examples, a powder having a particle size distribution with a D (50) of approx. 10 μm and a D (99) <63 μm was prepared from the molten solder glasses and processed to a dispensable paste with a binder. Homogenized powder and binder wounds with a three-roll mill. The binder is generally organic substances such. As nitrocellulose, ethylcellulose or acrylate binder. It generally has no further influence on the properties of the crystallized glass solder, but should be selected so that it can be completely burned out during the heating process.

Subsequently, the thermal characterization of the glass solders by means of a Heiztischmikroskopes. From the solder glass or composite in powder form to be characterized, a cylindrical specimen is pressed, which is heated on a ceramic base plate at 10 K / min. The changes in shape of the specimen are observed, with the temperature increasing for a non-crystallizing sample usually giving the following characteristic points, to which certain viscosities can be assigned: Sintering start: At this temperature, the grains of powder begin to fuse. As a result, the height of the sample body decreases. The logarithm of the viscosity is about 10 +/- 0.3. softening temp .: This temperature EW _K is characterized by an incipient rounding of the edges of the sample cylinder. The logarithm of the viscosity is about 8.2. Sphärischtemp .: The logarithm of the viscosity is about 6.1. Halbkugeltemp .: The specimen at this temperature has approximately the shape of a hemisphere. The logarithm of viscosity is about 4.6 +/- 0.1. Flow temperature: At this temperature, the height of the specimen is about 1/3 of the initial height. The logarithm of the viscosity is about 4.1 +/- 0.1. Crystallization temperature T _c : Peak crystallization temperature determined by differential thermal analysis (DTA), exothermic reaction

However, a significant deviation from this behavior is observed if crystallization already occurs during the slow heating of the specimen. In this case, the sample body can remain stable to a much higher temperature than the underlying base glass, and then exhibits a kind of melting point corresponding to the behavior of a crystalline solid, in which, unlike a glass, it makes a sudden transition to the liquid phase comes. In this case, a spherical temperature or a hemisphere temperature may not be determined.

After completion of the crystallization process, the transition temperature T _{g, K} and the thermal expansion α _{(20-300), K} in the temperature range from 20 to 300 ° C were also determined on the crystallized glass solder, the properties measured on the crystallized glass solder being characterized by the index K. are.

The thermal properties of the glass solders as determined by the hot-stage microscope and after crystallization are also summarized in Table 1.

The fact that a T _g can be determined in part from the thermal expansion curve indicates the presence of a residual glass phase. The slightly lower T _{g, K} compared to the amorphous solder glass can be explained by the depletion of SiO ₂ in the glass phase, since barium silicates (eg Ba ₅ Si ₈ O ₂₁ ) are formed.

By contrast, all examples B1 to B10 have the behavior desired according to the invention. These reach hemisphere temperatures well below 1100 ° C. The hemisphere temperature is also often referred to as the sealing temperature.

The crystalline content of sanbornite in glass solders according to Examples B6 to B10 when sintered at 835 ° C. and lasting for 120 minutes was investigated. It was found that B6 contained 50% by weight of Sanbornite, B8 contained 20% by weight of Sanbornite and B9 contained 24% by weight of Sanborite.

The inventors have also recognized that the glasses of Examples B3 to B10 are particularly suitable for laser joining processes, because they allow melting temperatures of less than 1100 ° C, since at larger process temperatures to connect to the glass solder and / or to be closed ceramic under the laser due the change of optical properties coupled (increase in the absorption coefficient) and it can lead to an undesirable jump in temperature increase.

When using laser radiation for joining the joint assembly is usually heated very quickly, with crystallization is largely suppressed. Within a few seconds to minutes, a stable joining compound can be obtained. Positive joining experiments were carried out with a diode laser (power 3 kW) and emission wavelengths of 808 nm and 940 nm. The starting glasses are stirred into a suspension as a powder and brushed onto the joining compound and then irradiated with the laser.

In oven processes, on the other hand, crystallization of the glasses occurs due to the longer residence times. The forming high-expansion crystal phase, for example Sanbornit, leads to an increase of the linear expansion coefficient. If the soldering carried out in furnace processes, so the glasses are particularly suitable for the addition of high-stretching oxide ceramics such. Zirconium oxide. The linear expansion coefficient α _{(20-300), K} correlates to a good approximation with the crystalline content of Sanbornit.

The value of α _{(20-300), K} in Example B7 is higher compared to B8, because in addition Fresnoit (barium titanate) crystallizes.

The composition of the glasses according to the invention is preferably chosen so that it does not lie in the SiO ₂ precipitation field during processing, ie during the joining process, but rather on the connecting line between a low-melting barium silicate phase and the ternary eutectic. This is also based on the in 1 illustrated phase diagram of the system BaO SiO ₂ -B ₂ O ₃ illustrates.

The glass solders of Examples B3 and B8 are particularly suitable for joining Al ₂ O ₃ ceramics and the glass solders of Examples B4 and B5 for joining ZrO ₂ ceramics.

The glass solders according to the invention can be either partially crystalline or amorphous. In the case of semicrystalline glasses, the addition of Al ₂ O ₃ and CaO prevents crystallization and the precipitation of undesired crystal phases. Also, crystallization can be completely suppressed, thus providing a stable amorphous glass solder, such as the absence of an exothermic signal in the DTA curve of Example B9 2 shows.

For the later use of the joint assembly, it is important that no further crystallization and a related change in property occurs. The HTXRD measurements show that in example B8 the crystallization with 24% by weight is already completely complete after 60 minutes and no further change in the phase balance occurs. The degree of crystallization changes only by 3% by weight within the first hour.

For the production of composites, the solder glass from Example B1 was also used as a base glass, wherein the powder of the base glass between 10% to 25% fillers were added. The same properties were determined on the resulting composites analogous to the filler-free solder glasses and summarized in Table 2 in a cross-comparison to the filler-free solder glass. Also shown in Table 2 is the linear thermal expansion coefficient α _{(20-750), K} , which characterizes the composite's thermal expansion properties in the temperature range from 20 ° C to 750 ° C. This value indicates that the thermal expansion is within the target range over the entire temperature range relevant for the processing. In addition, the value indicates that the sample has crystallized. The value can not be determined on the base glass from Example 5 without fillers since this has an EW _G of 730 ° C. and thus softens before reaching 750 ° C. In particular, in evaluating the thermocyclability of the materials, the coefficient of thermal expansion α _{(20-750), K is more} relevant than α _{(20-300), K.}

The comparison with B1 shows that in the case of addition of 10% 3YSZ or 25% BaSi ₂ O ₅ (sanbornite) the coefficient of thermal expansion α _{(20-300), K of} the composite is greater than that of the crystallized glass solder alone, while in the case the addition of 15% BaSi ₂ O ₅ the value is smaller. This proves that by selecting and by the amount of fillers both a positive or negative adjustment of the thermal expansion coefficient can be achieved.

The hemisphere temperatures and thus also the soldering temperatures are higher in the composites shown in Table 3 than in Example B1. However, in the case of the composites, the flow temperature is higher than that of Example B1. Table 2: Properties of composites based on Example B1 (hot-stage microscope) and after crystallization B1 90% B1 + 10% 3YSZ 85% B1 + 15% BaSi ₂ O ₅ 75% B1 + 25% BaSi ₂ O ₅ sintered beginning ° C 653 655 705 660 Softening temp. EW _K ° C 757 785 858 908 Spharischtemp. ° C 786 - 895 - Halbkugeltemp. ° C 853 877 1007 944 flow temperature ° C 906 931 1120 991 α _{(20-300), K} 10 ^-6 K ^-1 9.8 10.0 9.5 10.3 α _{(20-750), K} 10 ^-6 K ^-1 Not determinable, since already softened 14.2 12.7 13.2

The composites according to the invention were used to successfully produce joining compounds with a metallic interconnector lateral. First, the joint was heated at a heating rate of 5 K / min to 450 ° C and held at 450 ° C for 30 minutes. Subsequently, the joint was further heated at 2 K / min to 950 ° C and held for 30 minutes. Subsequently, the joint was cooled at 2 K / min to 860 ° C and held for 10 hours. Cooling to room temperature is also carried out at 2 K / min. During the joining process, the joint connection was subjected to a static weight (about 15 g / cm ² ).

The glass solders and composites according to the invention combine all the positive properties according to the object of the invention. The solder glass as a precursor can be produced by conventional melting processes with good melting behavior and not too high melting temperatures. It has a thermal expansion in the desired range and in particular no tendency to crystallize or spontaneous crystallization. Due to the composition, the formation of unwanted crystal phases is effectively prevented, which permanently enables stable low-stress joint connections.

The composites according to the invention can be adapted to the thermal expansion of the interconnector materials over a wide range by means of various fillers.

With the crystallizing glass solders and composites according to the invention joining compounds are obtained at low processing temperatures of about a maximum of 1100 ° C, which allow high operating temperatures of about 850 ° C. Furthermore, the good wetting of the interconnect materials by the slow crystallization only after the introduction of the solder permanently stable joint connections.

The solders of the invention have the advantage that they are suitable both for the compound with Al ₂ O ₃ - and for the compound with ZrO ₂ ceramics, without the glass having to be adapted with fillers, because the linear thermal expansion coefficient α _{( 20-300), K} can be controlled by the process control during the melting process.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 19857057 C1 [0008]
• US 6532769 B1 [0009]
• US 6430966 B1 [0009]
• DE 102005002435 A1 [0010]
• DE 10122327 A1 [0011]

Claims (18)

Glass solder for high temperature applications containing (in% by weight on an oxide basis) BaO 42-60 SiO ₂ 24-40 B ₂ O ₃ 0-15 SrO 0-18 RO 0-10 R ₂ O ₃ 0-10 RO ₂ 0-5, wherein RO is at least one alkaline earth oxide selected from the group MgO and / or CaO and / or ZnO and / or BeO, R ₂ O _{3 is} an oxide selected from the group Al ₂ O ₃ and / or Ga ₂ O ₃ and / or In ₂ O ₃ and / or Y ₂ O ₃ and / or La ₂ O ₃ , RO _{2 is} an oxide selected from the group TiO ₂ and / or ZrO ₂ and / or HfO ₂ . A glass solder according to claim 1, wherein the sum of SrO and RO is up to 20% (in wt% on oxide basis), preferably from 2% to 15%. Glass solder according to at least one of the preceding claims, containing (in% by weight based on oxide) BaO 42-52 SiO ₂ 24-31 B ₂ O ₃ 0-11 SrO 14-18 CaO 0-5 MgO 0-10 R ₂ O ₃ 0-10 RO ₂ 0-5 ΣCaO + MgO + R ₂ O ₃ + RO ₂ 0-19 Glass solder according to at least one of Claims 1 to 3, containing (in% by weight based on oxide) BaO 47-50 SiO ₂ 35-39 B ₂ O ₃ 5-15 CaO 0-10 MgO 0-10 TiO ₂ 0-5 ZrO ₂ 0-5 Glass solder according to claim 4, wherein the molar ratio of the contents of SiO ₂ / BaO ≤ 2.5, preferably ≤ 2. Glass solder according to at least one of the preceding claims, additionally containing in each case (in% by weight based on oxide) up to 0.5% V ₂ O ₅ and / or Sb ₂ O ₃ and / or CoO. Glass solder according to at least one of the preceding claims, which crystallizes at least partially, with a thermal expansion coefficient in the glassy state α _{(20-300), G} of 6 · 10 ^-6 K ^-1 to 11 · 10 ^-6 K ^-1 and / or im crystallized state α _{(20-300), K} from 8 · 10 ^-6 K ^-1 to 12.6 · 10 ^-6 K ^-1 . Glass solder according to at least one of the preceding claims with a hemispherical temperature of 850 ° C to 1100 ° C. Glass solder according to the embodiments listed in Table 1. A composite comprising a glass solder according to at least one of the preceding claims and additionally (in% by weight based on oxide) up to 35% of a crystalline filler. A composite according to claim 10, wherein the crystalline filler comprises sanbornite and / or 3YSZ and / or wollastonite and / or enstatite. Composite according to at least one of claims 10 to 11 having a coefficient of thermal expansion in the crystal _phase α _{(20-750), K} of 9.5 · 10 ^-6 K ^-1 to 14.5 · 10 ^-6 K ^-1 . A composite according to any one of claims 10 to 12 having a hemispherical temperature of 850 ° C to 1020 ° C. Glass solder or composite according to at least one of the preceding claims, _wherein the difference in the thermal expansion α _(20-300) before and after the crystallization process is less than 2 · 10 ^-6 K ^-1 , and preferably less than 1 · 10 ^-6 K ^-1 is. Use of a glass solder and / or composite according to at least one of the preceding claims for the production of high-temperature joining compounds, in particular for fuel cells. Use of a glass solder and / or composite according to at least one of claims 1 to 14 in sintered bodies with high temperature resistance. Use of a glass solder and / or composite according to at least Eifern of claims 1 to 14 for the production of films with high temperature resistance. Use of a glass solder and / or composite according to at least one of claims 1 to 14 for joining Al ₂ O ₃ and / or ZrO ₂ ceramics.

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